I've been experiencing data corruption/loss in Postgresql 7.4.2.
I tracked this down to altering tables. After I alter a table, I get data
loss (fields becoming NULL with no reason!) unless I restart immediately
the database server. After the restart all seems OK (but the data which
was lost, is gone, I just don't loose any more). I'm a bit scared though
that this might not be enough, so I'd appreciate comments. Is this a
known bug which has been fixed in later releases ?
I managed to extract a simple sequence of SQL instructions which reliably
causes data corruption/loss on my 7.4.2 (fedora core 2 default install). I
found that all machines I've access to are 7.4.2, so I couldn't test it on
later releases. Apologies if it has already been fixed, I didn't find
references to a bug fix for it.
Thanks
/*
* Nicola Pero, November 2004
*
* Test which demonstrates data corruption in Postgres
* when modifying tables then using plpgsql functions.
*/
/* We create a basic table. */
CREATE TABLE MyTable (
/* An index. */
ID SERIAL,
PRIMARY KEY (ID),
/* A value. */
CountA INT DEFAULT 0
);
/* We create a stored procedure to manipulate a record in the table. */
CREATE FUNCTION DO_SOMETHING(integer,integer)
RETURNS INTEGER AS '
DECLARE
BEGIN
UPDATE MyTable SET CountA = CountA + $1 WHERE ID = $2;
RETURN 0;
END' LANGUAGE 'plpgsql';
/* We insert a single record in the table. */
INSERT INTO MyTable (CountA) VALUES (1);
/* We try out that the stored procedure works. */
SELECT DO_SOMETHING (1, 1);
/* Print out the table now. */
/* On my system, I get:
* id | counta
* ----+--------
* 1 | 2
* (1 row)
*/
SELECT * FROM MyTable;
/* OK. Now we modify the table. We add a column with value 0. */
ALTER TABLE MyTable ADD COLUMN CountB INT;
ALTER TABLE MyTable ALTER COLUMN CountB SET DEFAULT 0;
UPDATE MyTable SET CountB = 0;
/* Now put a value in CountB. */
UPDATE MyTable SET CountB = 12;
/* Print out the table with the new column added. */
/* On my system, I get:
* id | counta | countb
* ----+--------+--------
* 1 | 2 | 12
* (1 row)
*/
SELECT * FROM MyTable;
/* Alter the value in the CountA column using the stored procedure. */
SELECT DO_SOMETHING (1, 1);
/* Print out the table again. */
/* On my system, I get:
* id | counta | countb
* ----+--------+--------
* 1 | 3 |
* (1 row)
*
* note how the value in the CountB column has been
* destroyed/corrupted into NULL!!
*/
SELECT * FROM MyTable;
